Fluoroalkyl perfluorovinyl ethers of the formula R.sub.f --CF.sub.2 --O--CF.dbd.CF.sub.2, wherein R.sub.f is fluorine or a fluorine-containing organic radical, have found extensive use as co-monomers for preparation of fluoroplastics and fluoroelastomers. Fluoroalkyl perfluorovinyl ethers are known to co-polymerize with alkenes such as ethylene, tetrafluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, propene and hexafluoropropene. Of particular interest and significant application are co-polymers formed by co-polymerization of perfluoroalkyl perfluorinated ethers with tetrafluoroethylene and/or hexafluoropropylene. These co-polymers are often referred to as perfluoroalkoxy co-polymers, and are useful in producing high-quality electrical insulation and molded components. A general review of perfluoroalkoxy co-polymers occurs in a review article titled "Organic Fluoropolymers" by Carlson et al, found in Ullman's Encyclopedia of Industrial Chemistry, Fifth Edition, p. 393.
The prevalent method found in the art for preparation of fluoroalkyl perfluorovinyl ethers (see Kirk-Othmer Encyclopedia of Chemical Technology, Fourth Edition, page 672) involves firstly the reaction of a fluoroalkyl carboxylic acid fluoride with hexafluoropropylene oxide to form an intermediate fluoroalkyl 2-alkoxypropionic acid fluoride as shown by the following equation: ##STR1## wherein R.sub.f is fluorine or a fluorine-containing organic radical.
This intermediate fluoroalkyl 2-alkoxypropionic acid fluoride, after purification by distillation or other means, is then defluorocarbonylated by treatment with a dry alkali carbonate to form a fluoroalkyl perfluorovinyl ether as shown by the following equation: EQU R.sub.f --CF.sub.2 --O--CF(CF.sub.3)--COF+Na.sub.2 CO.sub.3 .fwdarw.Rf--CF.sub.2 --O--CF.dbd.CF.sub.2 +2CO.sub.2 +2NaF
where Na.sub.2 CO.sub.3 is used as an example of the alkali carbonate. In a typical process, the solid impurities such as NaF and unreacted Na.sub.2 CO.sub.3 are then removed by filtration as by passing through a bag filter, and the CO.sub.2 is removed by scrubbing with an alkali solution such as NaOH or KOH solution to form the corresponding alkali carbonate. KOH is preferred because of improved solubility. Water may then be removed as by passage through molecular sieves or by other means, and the dried crude fluoroalkyl perfluorovinyl ether is further purified as required for its intended use, typically by distillation to remove high and low-boiling impurities.
The removal of CO.sub.2 by alkali scrubbing is costly for a number of reasons. Since there is a large amount of CO.sub.2 produced, there is a large consumption of alkali and a large waste disposal problem for the alkali carbonate solution which is contaminated with fluorine-containing organic impurities. In addition, there is a significant yield loss, perhaps 1 to 5%, of expensive fluorochemical product caused by a combination of solubility in the waste scrubbing solution and some reactions of the fluoroalkyl perfluorovinyl ether with the alkali.
There is a need for a method for separation of part or essentially all of the CO.sub.2 from the fluoroalkyl perfluorovinyl ethers reaction product with a minimum or elimination of alkali scrubbing, and without introducing new chemicals into the system.
It is also known to carry out polymerizations of fluorinated monomers in media comprising CO.sub.2. See, for example, U.S. Pat. No. 5,674,957. Unreacted monomers from such processes are desirably recovered from mixtures with CO.sub.2 for recycle to the polymerization reaction.